Great Basin Water Supply Outlook, May 1, 2013

Note: This publication is scheduled for revision. If you have feedback on content, format, or publication frequency, please contact us.
Prepared by Brent Bernard
NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents

Great Basin Summary






*Median of forecasts within each basin.


Bear Basin Conditions




* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Weber Basin Conditions




* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Six Creeks Basin Conditions




* Percent usable capacity, not percent average contents.
Click for multi-month Graph.

Utah Lake Basin Conditions




* Percent usable capacity, not percent average contents.
Click for multi-month Graph.


Bear Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		10%
Exceedance
Volume
Bear
Utah April-July55 75 67 93
May-July40 70 67 80
Woodruff Narrows Rsvr, Abv April-July50 72 60 100
May-July25 67 64 75
Montpelier, Nr, Stewart Dam, Blo * April-July11 45 25 75
May-July20 29 20 80
Smiths Fork
Border, Nr April-July42 56 63 69
May-July33 50 63 67
Logan
Logan, Nr, State Dam, Abv April-July45 71 64 90
May-July37 58 60 83
Blacksmith Fork
Hyrum, Nr, Upnl Dam, Abv April-July14 22 51 35
May-July10 16 52 36
Little Bear
Paradise April-July5 14 30 26
May-July4 9.6 30 21

*Regulated Forecast, i.e. Observed flow uncorrected for upstream diversion.

Weber Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		10%
Exceedance
Volume
Weber
Oakley, Nr April-July55 80 68 100
May-July37 75 71 83
Rockport Res, Wanship, Nr April-July50 75 60 100
May-July25 67 62 85
Coalville, Nr April-July50 75 58 105
May-July20 65 60 70
Chalk Ck
Coalville April-July11 24 59 37
May-July3 21 62 31
Weber
Echo Res, Echo, At April-July55 97 58 130
May-July25 85 61 104
Lost Ck
Lost Ck Res, Croydon, Nr April-July1.5 3.9 29 5.5
May-July0.5 2.3 24 5
East Canyon Ck
East Canyon Res, Morgan, Nr April-July6 12.5 46 19
May-July2.4 8.8 47 18.1
Weber
Gateway April-July75 152 48 230
May-July36 124 52 179
Sf Ogden
Huntsville, Nr April-July8 18.8 34 35
May-July5.6 12.6 32 31
Ogden
Pineview Res, Ogden, Nr April-July11 36 32 70
May-July5 21 29 50


Six Creeks Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		10%
Exceedance
Volume
Little Cottonwood Ck
Salt Lake City, Nr April-July19 25 66 31
May-July17 23 66 26
Big Cottonwood Ck
Salt Lake City, Nr April-July14.5 22 61 28
May-July10.3 20 63 26
Mill Ck
Salt Lake City, Nr April-July1.8 2.9 45 4.1
May-July1 2.4 44 4.2
Dell Fk
Little Dell Res April-July1 2.9 53 4.5
May-July0.3 2 51 4.4
Parleys Ck
Salt Lake City, Nr April-July2.2 5.8 41 10
May-July1.1 4.2 40 10.3
Emigration Ck
Salt Lake City, Nr April-July0.1 1.2 30 2.3
May-July0.1 0.77 29 2.1
City Ck
Salt Lake City, Nr April-July3 4.3 56 5.8
May-July1.7 3.6 55 6.4
S Willow Ck
Grantsville, Nr April-July1.9 2.5 81 3.2
May-July1.7 2.4 89 3.1


Utah Lake Specific Site Forecasts (kaf)

Click site name for graph.
Forecast
Period		90%
Exceedance
Volume		50%
Exceedance
Volume		Percent
Average		10%
Exceedance
Volume
Spanish Fork
Castilla, Nr April-July8 22 32 38
May-July4.8 17 31 30
Provo
Woodland, Nr April-July49 65 65 86
May-July30 60 67 80
Hailstone, Nr April-July43 72 65 89
May-July29 66 68 82
Deer Ck Res April-July41 71 56 91
May-July32 60 58 78
American Fork
American Fork, Nr, Up Pwrplnt, Abv April-July6 12 39 17
May-July5 11 39 17
West Canyon Ck
Cedar Fort, Nr April-July0.2 0.61 35 1.2
May-July0.3 0.6 39 1.8
Jordan
Utah Lake, Provo, Nr April-July70 155 48 235
May-July40 112 45 205

Differences between the full period forecasts and the residual forecasts may not exactly equal the actual observed volumes due to rounding conventions (see Definitions section).

Great Basin End of Month Reservoir Contents (kaf)

EOM
Contents		Percent
EOM
Average		Percent
Usable
Capacity		Last Year
EOM		Last Year
%Average		EOM
Average		Usable
Capacity
untitled Bear
Woodruff Narrows Res, Woodruff, Nr 17.5 39 31 58.8 131 45.0 55.8
untitled Bear River
Bear Lake, Nr Lifton 961.1 125 74 1189.4 154 770.8 1302.0
untitled Little Bear
Hyrum Reservoir 14.7 103 96 14.7 103 14.2 15.3
untitled Weber
Rockport Res, Wanship, Nr 37.7 94 68 46.7 116 40.1 55.2
Echo Res, Echo, At 34.1 63 46 70.7 130 54.3 73.9
untitled Lost Ck
Lost Ck Res, Croydon, Nr 17.2 129 77 22.7 171 13.3 22.5
untitled East Canyon Ck
East Canyon Res, Morgan, Nr 33.9 86 69 49.7 126 39.5 49.5
untitled Sf Ogden
Causey Res 6.9 136 97 7.1 142 5.0 7.1
untitled Ogden
Pineview Res, Ogden, Nr 69.9 88 63 110.2 138 79.7 110.1
untitled Jordanelle Dam
183.8 73 57 277.1 110 251.3 320.3
untitled Provo
Deer Ck Res 141.4 114 94 148.9 121 123.5 149.7
untitled Dell Fk
Little Dell Res 12.1 -99 59 11.6 -99 -9999.0 20.5
untitled Jordan
Utah Lake, Provo, Nr 772.1 93 89 861.6 104 827.8 870.9
untitled
TOTAL 2290.3 101 75 2857.7 126 2264.6 3052.8

Precipitation Maps




Definitions

10% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 10% chance of being exceeded. Previously referred to as "Reasonable Maximum Forecast".

50% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 50% chance of being exceeded. Previously referred to as "Most Probable Forecast".

90% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 90% chance of being exceeded. Previously referred to as "Reasonable Minimum Forecast".

Acre-Foot (af): The volume equal to one acre covered one foot deep (43,560 cubic feet). See kaf below.

Average: The arithmetic mean. The sum of the values divided by the number of values. Values from 1981-2010 are used for this publication.

Categories: Much Above Average=Greater than 130%, Above Average=111-130%, Near Average=90-110%, Below Average=70-89%, Much Below Average=Less than 70%.

CBRFC: Colorado Basin River Forecast Center.

Forecast Period: The period from April 1 through July 31, unless otherwise noted.

kaf: Thousand Acre-Feet. See Acre-Foot above.

Inflow: The volume of water that flows into a reservoir or lake.

Median: The middle value of an ordered set of values. Half of the values are higher and half of the values are lower. When the set contains an even number of values the median is the average of the two middle numbers.

NOAA: National Oceanic and Atomospheric Administration.

NWS: National Weather Service.

Rounding Conventions:
RangeRound to
0-1.990.01
2.0-19.90.1
20-1991.0
200-9995.0
1000+3 significant digits


Streamflow: The volume of water that flows past a specific stream site.

Water Year: The 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends. Thus, the year ending September 30, 2008, is called the "2008 water year."


Additional Information

Water supply forecasts take into consideration present hydrometeorological conditions and use average basin temperatures and precipitation for the forecast period. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty becomes known and monthly forecasts become more accurate. For more information on the tools we use, consult Water Supply Forecasting Tools.

Volume forecasts represent adjusted flows; that is, observed flows with upstream water use taken into account. Adjusted flows will closely approximate natural or unimpaired flows. However, not all upstream diversions or impoundments are measured or quantifiable. For specific adjustments used with each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through May by the Colorado Basin River Forecast Center. It represents a coordinated effort between the National Weather Service, Natural Resources Conservation Service, Bureau of Reclamation, U.S. Geological Survey and local water district managers.

Note: Data used in this report are provisional and are subject to revision.

For more information, or to be included on the mailing list, please contact:

Colorado Basin River Forecast Center
2242 W North Temple
Salt Lake City, UT 84116
(801) 524-5130
www.cbrfc.noaa.gov


Hydrologist: Brent Bernard